Mucocele Causing Diplopia: A Rare Complication After Endoscopic Sinus Surgery

Paranasal mucoceles are benign, mucus-filled lesions that develop due to obstruction of sinus drainage pathways. Although commonly arising in the frontal and ethmoidal sinuses, significant orbital extension is rare. Such expansion may lead to symptoms including diplopia, proptosis, and visual impairment. This report describes the case of a 74-year-old woman presenting with acute proptosis, severe orbital pain, and longstanding diplopia caused by a large intra-orbital ethmoidal mucocele. The mucocele was successfully managed by endoscopic sinus surgery (ESS). Frontal sinus drainage was subsequently restored. Postoperative imaging confirmed complete resolution of the mucocele, although diplopia only partially improved. The mucocele likely resulted from postoperative scarring and impaired sinus drainage. Prompt endoscopic intervention effectively re-established ventilation, preventing further orbital compromise. Clinicians should remain aware that mucoceles may present after ESS and can cause substantial orbital morbidity. Early recognition and endoscopic management are essential to prevent permanent visual sequelae.